Telephone system



s. F. NELSON E1- AL TELEPHONE SYSTEMl sept. 22, 1936.

Filed June 15, 1935 '7 sheetssheet 1 WEA/70,185.5 NELSON FF SH/PL Ey. By

F/G. 3 676.5 F/G. 7

ATTORNEY Sept. 22, 1936.y s. F. NELSON ET AL. 2,054,910

TELEPHONE SYSTEM Filed June 15, 1935 l '7 Sheets-Sheet 2 5f.' NELSON /NVENTORS HT sH/PLEV A TTORNEV Sept. 22,1936. s. F. NELSON ET A1. 2,054,910

TELEPHONE SYSTEM Filed June 15, 1935 *l sheets-sheet 3 f F/G.l4

v 5f Naso/v /NVENTORS FF sH/PLEr A TTOR/VEV Sept. 22, 1936. s. F. NELSON E1- Al. 2,054,910

TELEPHONE SYSTEM Filed 4.June 15, 1935 7 sheets-sheet 4 sf NELSON /NVENTORS' E E sH/PL 5y AHORA/5y sept. 22, 1936 S. F. NELSON ET AL TELEPHONE SYSTEM Filed June l5, 1955 A '7 SheebS-Sheet 5 5f /vgL 50N f.' E SH/PL Ey /Nl/E/VTORS:

Sept. 22, 1936. s. F. NELSON E1- Al. 2,054,910

l TELEPHONE SYSTEM l l Filed June 15, 1935 7 sheetswseet e' 5.5 NELSON /NVEVNTORS'E/- sH/PLEV Sept. 22, 19,36. s. F. NELSOQ TVAL l 2,054,910

TELEPHONE SYSTEM Filed June 15, 1955 7 sheets-sheet '7 823 ...f- /Nl/E/VTORS BV WM Patented Sept. 22, 1936 UNHTED STATES PATENT OFFICE TELEPHONE SYSTEM Application June 15, 1935, Serial No. 28,860

Y 11 claims.

This invention relates to telephone systems and particularly to systems of the character in which automatic switching apparatus is employed for establishing connections. l The object of the invention is to enable a more eicient and economical use of the switching and controlling equipment in the establishment of connections through group-selecting stages comprising switches of the cross-bar type which receive the successive series of designation impulses directly from the subscribers dial or other sending device.

It has been suggested heretofore to control group-selecting switches of the cross-bar type by sending the digital impulses directly to the switches at the successive stages as distinguished from recording the whole designation in a sender or marker which in turn controls the successive switches. Such an arrangement is disclosed in the patent to Clark, No. 1,567,242 of December 29, 1925.

The present invention secures advantages over rthese prior systems by the use of a more efficient connecting arrangement in which an incoming circuit is selectively connected to an outgoing circuit through primary and secondary switches, these switches being interconnected by link circuits and controlled and operated by associated equipment that receives the digit impulses directly from the dial.

Another feature o-f the invention'is a system in which each group-selecting stage comprises a plurality of primary and a plurality of secondary cross-bar switches interconnected by iinks, a plurality of incoming circuits or trunks appearing in each of the primary switches, the successive digital series being sent directly to the controlling apparatus associated with each successive stage as the connection progresses from stage tostage, and in which all of the trunks incoming to a particular primary switch are served by the same digit receiving mechanism forming a part Vof the controlling apparatus associated with that stage.

Another feature of the invention is a circuit arrangement such that if a plurality of calls reach a group-selecting stage simultaneously they are disposedof one at a time. This prevents interference between two incoming calls seeking trunks in the same outgoing group, and it also enables an incoming call at one primary switch to reach any idle outgoing trunk through any available link without interference from an incoming call at some other primary switch that may be seeking connection to a trunk in either the same or another outgoing trunk group. l

Another feature is an arrangement for testing the outgoing trunks of a group and the interconnecting link circuits in which each outgoing trunk is tested in conjunction with the link circuit that interconnects the secondary switch in which such outgoing trunk appears andthe particularprimary switch in which appears the calling incoming trunk, and in which the busy condition of the link is determined by the fact that the test circuit therefor is completed through the closed contacts 'D of the link at the primary selector switch. The test relay that tests a particular outgoing trunk is also applied to all links extending from the respective primary switches to the secondary switch in which the outgoing trunk appears, but since 3 only one call can be in progress at a time a complete circuit for the testing relay can be closed only through the primary switch in which appears the call that is in progress.

A further feature is a circuit arrangement for 2O operating the magnets of the switches in which a battery potential is applied to the magnets of all link circuits incoming to the particular secondary switch in which appear the idle outgoing trunk to be selected for use at the same time that 25 the opposite potential of the battery is applied to the magnets of al1 links outgoing from the calling primary switch to the several respective secondary switches. Since one of these links interconnects the primary and secondary switches involved, 30 their magnets are operated in series to complete the connection through the stage to the groupselecting stage beyond.

These and other features of the invention will be explained more fully in the following detailed 35 description, which should be taken in connection with the accompanying drawings. e

The following description Will cover only the operation of an intermediate group-selecting stage of a telephone system embodying this in- 40 Vention since other intermediate stages are practically identical, differing only in the quantities of apparatus required. The initial or line-finder stage, as well as the final or connector stage, may be assumed to be of whatever type is best 45 suited to perform the particular functions of these said stages and may consist of any combination of crossbar switches, Strowger switches, Keith line switches or any other suitable equipment, the functions and operation of which are Well 50 known to the art.

Figure l of the accompanying drawings illustrates diagrammatically the manner in Vwhich the groups of primary and secondary switches of any group-selecting stage are interconnected. 55

Fig. 2 shows the invention applied to a plurality of group-selecting stages. Y

Fig. 3 illustrates, in part, one switch of the primary switch group in which appear three trunks TI, T2 and T3 incoming from the preceding stage. Associated with this primary switch Pl is shown the level selector LSI which, under control of dial impulses, selects a linktrunk selector corresponding to the dialed digit.

Fig. 4 illustrates, in part, two other primary switches P2 and P3 together with their associated level selectors LSE and LS3 respectively. Appearing in switch P2 are trunks Tl, T5 and T6 inco-ming from the preceding stage. In switch P3 appear incoming trunks Tl, T3 and T9. The individual trunk relays for trunks T4 to T9, inclusive, as well as the relays for switches P2 and P3 and the magnets and springs for controllingY level selectors LSE and LS are not shown since these trunks, switches and level selectors are identical with, and function in the same manner as trunks Ti to T3 inclusive, switch Pl, and level selector LSl respectively.

Fig. 5 illustrates the iink-trunk selector LTSI associated with the trunks outgoing from the upper level of the secondary switches to the succeeding stage. Fig. 5 also shows a link circuit selector LCS, common to all link-trunk selectors, which selects an idle outgoing trunk in the proper level on a secondary switch to which there is an idle link from the primary switch.

Fig. 6 illustrates two other link-trunk selectors LTSZ and LTS3 which are respectively associated with the trunks outgoing from the middle and lower levels of the secondary switches.

Fig. 7 illustrates, in part, one switch of the secondary switch group, in which appear the trunks Tll, TiZ, and Tit outgoing to the succeeding stage.

Fig. 8 illustrates, in part, two other switches of the secondary switch gro-up, in which appear outgoing trunks Till to TiS, inclusive.

Fig. 9 shows how Figs. 3, 4, 5, 6, 7, and Bare to be arranged with respect to each other in disclosing the switches and associated equipment which comprise an intermediate group-selecting stage.

Switches Pl, P2, P3, P5, Sl, S2, S3, and S5 shown in Figs. i, 2, 3, 4, "I, and 8 are of the crossbar type and consist brieily off a plurality of sets of contacts arranged in horizontal and vertical rows or units. Associated with each horizontal row of contact sets is a horizontal operating magnet under control of which the said horizontal contact sets are prepared for operation. Associated with each vertical row of contact sets is a vertical magnet under control of which any set of contacts in that vertical row, after being prepared by the operation of its respective horizontal magnet, is operated and held in that position until the release oi the vertical magnet takes place. Fora more detailed explanation of the construction and operation of these crossbar switches reference may be made to the application of J. N. Reynolds Serial No. 702,453, led December 15 1933, granted as Patent 2,021,329, Nov. 19, 1935.

Referring now to Fig. l, for the purpose of simplicity only such portions of three of the primary and secondary switches are shown as is required to illustrate, in general, the manner in which a connection is extended through a group-selecting stage. It will be apparent, however, that the system is applicable to any number of primary and secondary switches and that these said switches may be comprised of any number of horizontal and vertical rows or units of contact sets.

Appearing in the vertical row or units of contact sets of the primary switches Pl, P2 and P3 are trunks such as Ti, T2 and T3, incoming from the preceding stage. The horizontal rows of contacts of primary switch Pi connect to the first Vvertical rows of contacts on the secondary switches SI, S2 and S3 over links Li, L2 and L3, respectively. Similarly, the horizontal contact rows of primary switch P2 connect to the second rows of vertical contacts on the secondary switches over links L4, L5 and L6, and the horizontal contacts of primary switch P3 connect to the third vertical rows of contacts on secondary switches Sl, S2 and S3 over links Ll, L8 and L9. Each incoming trunk, such as trunks TI, T2 and T3, therefore has access to each secondary switch and, through the secondary switches, may be extended to the succeeding stage over outgoing trunks such as trunks Tl l, Ti2 and Tl3. While a single link is shown from a primary to a secondary switch, it will be understood that the invention is not so limited and that more than one link could be used if desired.

Associated with each horizontal row of sets of contacts on the primary switches Pl, P2 and P3 is a horizontal operating magnet, such as magnets lill, IUZ and 103, under control of which, in conjunction with the operation of a vertical operating magnet (not shown), a particular set of contacts is operated. Associated with each vertical row of contact sets on the secondary switches Sl, S2 and S3 is a vertical operating magnet, such as magnets H04, |535 and H06, under control of which, in conjunction with the operation of a horizontal magnet (not shown), a particular set of contacts of the secondary switch is operated.V Y

Each primary switch horizontal magnet connects to a vertical magnet of a secondary switch over a conductor such as conductors itl, H88, |09 and I l2. Associated with each primary switch is a relay, such as relay i i@ of switch Pl, which connects battery to the windings of all horizontal magnets of a particular primary switch. Similarly, associated with each secondary switch is a relay, such as relay Il l of switch Si, which connects ground to the windings of all vertical magnets of a particular secondary switch. Selection of an idle outgoing trunk in the proper level of a secondary switch to which there is an idle link from the primary switch is made under control of a link-trunk selector and a link selector (not shown in this gure) the functions and operation of which will later be set forth in detail.

A call extended to this stage over incoming trunk TI may be extended to the succeeding stage over trunks Tl I, Tl2 or TIS outgoing from the secondary switches Si, S2 or S3 respectively, depending upon the selection made by the linktrunk selector which is associated with primary switch Pl at that time. Assuming, for example, that idle trunk TH Vis selected, horizontal magnet IDI of the primary switch Pl energizes in series with vertical magnet Hill of the secondary switch SI, over conductor il, upon the operation of relaysY HD and Ill. In energizing, magnet li, in conjunction with the operation of a vertical magnet (not shown) causes the upper set of contacts in the first vertical row of switch Pl to operate. Similarly, magnet lilll, in conjunction with a horizontal magnet (not shown), causes the upper set of contacts in the rst vertical row of switch `SI to operate. The connection incoming over trunk TI is therefore extended to the succeeding stage over outgoing trunk TII,

over the aforementioned operated sets of con-` tacts of switches PI and SI.

Should idle trunk TIZ be selected, magnets |02 of switch PI and of switch S2 are energized over conductor |08, and the connection extends from trunk TE, over the middle set of contacts of the first vertical row of switch PI, link L2, and the upper set of contacts of the first vertical row of switch S2 to the succeeding stage over outgoing trunk Tii.. As a further illustration, assume that a call is extended tothis stage over the incoming trunk T3 and that the link-trunk selector (not shown) associated with switch P3 at this time selects idle trunk TIS. Horizontal magnet II3 oi switch P3 and vertical magnet I I4 of switch S3 are energized in series, over conductor I I2, upon the operation of relays II5 and H0, and the call is extended to the succeeding stage over the lower set of contacts of the rst vertical row of ccntacts of switch P3, link L0, over the upper set of contacts of the third vertical row of contacts of switch S3, and over the outgoing trunk TI3. It will be noted that, although battery is connected simultaneously to all horizontal magnets of a particular primary switch at the same time that ground is connected to all vertical magnets of a secondary switch, only one primary switch horizontal magnet and one secondary switch vertical magnet can operate, in series, since each link from any primary switch horizontal magnet leads to a separate secondary switch.

In Fig. 2 a calling line |30 having a dial ISI is shown terminating in a line switch I32 and a called line |33 terminating in a connector i3d. For the purpose of illustration only two intermediate group stages are shown. The rst of these comprises primary switches PI and secondary switch SI, and the second stage includes primary and secondary switchesP5 and S5. There may, of course, be other stages.

Referring now to Figs. 3 to 8 inclusive, the mam ner in which a call is extended through the groupselecting stage illustrated therein will be considered in detail. As hereinbefore set forth, a stage may consist of any desired number of primary and Y secondary switches and each switch, in turn, may

be composed of any convenient number of horizontal and vertical rows or units of cont-act sets.

` The group-selecting stage herein disclosed is as sumed to consist of ten primary and ten secondary switches, each switch having ten horizontal and ten vertical rows or units of contacts. For clarity of illustration and description, only the first, second and tenth switch of each of the group ci" ten primary and ten second switches are shown. ln addition, only the first, second and tenth rows of horizontal and vertical sets of contacts for each of the switches illustrated are shown. Three link-trunk selectors are illustrated, one being Mw scciated with the trunks outgoing from each of the secondary switches shown. lt should 'ce understood however that, since it is assumed that there are ten` horizontal rows or levels on each switch, there are also ten link-trunk selectors, one being associated with the trunks outgoing from each of the ten levels of the secondary switches.

Assume now that a call is extended to this group-selecting stage over the incoming trunk TI of Fig. 3. As soon as connection is established through the preceding stage, relay 30| operates in a circuit from batt-ery through its upper winding, over the lower back contact of vertical magnet 302, ring conductor 303 of trunk TI, ring conductor of the preceding stages, over the subscribers station loop (not shown) ,tip conductor of the preceding stages, tip conductor 300 of trunk TI, middle armature and back contact of magnet 302, lower winding of relay 30|, normallyr closed make-before-break contacts of relay 305 to ground. In the irst .group-selecting stage, the operating ground for relay 30|, instead of being connected directly to the back contact of the make-before-break contacts of relay 305 as in this case for an intermediate stage, is supplied through one winding of a coil through which a dial tone is induced to provide the calling subscriber with an indication that the circuit is ready for dialing. Relay 30|, in operating connects ground over its inner front contact to the lower armature of the off-normal springs 305 associated with the level selector LSI, and also operates relay 30'? in an obvious circuit, Relay 30?, in operating, connects ground over its upp-er inn-er front contact to sleeve conductor 303 of trunk TI, and also connects ground over its upper outer iront contact, over the neXt-to-inner back contacts of magnets 332, 309 and 3|0 to the respective sleeve conductors 308, 3|| and 3I2 of the incoming trunks TI, T2 and T3. This ground on the sleeve conductors of all of the incoming trunks provides for making this primary switch busy so that no other call can be extended to it until the call which has come in over trunk TI is extended to the succeeding stage. Relay 30?, in operating, also partially closes the operating circuit for vertical magnet 302, partially closes the locking circuits for relays 305 and 3I3, and closes, in part, the operating circuit for rotary magnet 3M of switch LSI.

Assuming that the calling subscriber dials the digit 2, relay 30| releases and reoperates twice in response to the two corresponding open intervals in the subscribers loop. Relay 301, being of the slow-to-release type, remains operated during the intervals in which the circuit through its winding is opened by the release of relay 30|. Each release of relay 30| energizes rotary magnet 3M of the level selector LSI in a circuit from .ground over the back contact of relay 30|, lower outer front contact o relay 30'I, left back contact of relay 3I3, to battery through the winding ci magnet 3M. Each operation of magnet 3M causes brushes 3I5 and 3|5 to advance one step over the contacts of their associated terminal banks. lin response to the two releases of relay 30|, corren sponding to the open pulses of the digit 2, brushes 3I5 and 3I6 therefore contact the second termi nal of their respective terminal banks. On the rst operation of magnet 3M the off-normal springs 300 operate, partially closing the circuit for the level selector release magnet 3 I 'I over their upper front contact, and partially closing the operating circuit for relay SIB over their lower front contact. When relay 30| reoperates at the conclusion of the dial pulses, .ground over its inner front contact completes the operating circuit for relay 3i8 which is of the slow-temperate type to prevent its operation during the dialing interval.

Relay 3Ii, in operating, operates relay SIS in an obvious circuit.v and connects ground over its right outer front contact and over the right back contact of relay 305 to the winding of relay Relay 3 3, in operating, locks over its right inner front Contact to ground over a previously traced circuit, and opens the circuit to the winding of Y magnet 3 I0.

A pair of sequence relays, such as relays 3|9 and 32S, 4|0 and 420, and 449 and 450, are associated with each primary switch of the group. The operating circuits for these relays extend over a chain circuit through the entire group of switches in such manner that only one pair of relays can operate at a time. Ground is connected over the normally closed right contacts of relay 3|9 of the first primary switch of the group,

over the normally closed right contacts of relay i9 and of the corresponding relays of the other intermediate switches of the group (not shown) to the right front contact of relay 449 of the last switch of the group. The operation of only one relay, such as relay 3|9, is effective at any one time since, by its operation, relay 360 removes the ground from the chain circuit and from the right contacts of the corresponding relay of each succeeding switch of the group. Similarly, battery is connected to the winding of relay 449 of the last switch of the primary group and over the left back contact of relay 450 to the winding and left back contact ofthe corresponding relays of each preceding switch, finally connecting to the winding of relay 3|9 of the rst primary switch of the group. The operation of relay 450, or of the corresponding relay of any intermediate switch, removes the battery from the windings of the relays corresponding to relay 3|9 and relay 4|0 in all switches preceding that switch on which relay 450, or its corresponding relay, operated.

With ground connected to the winding of relay 3|0 by the operation of relay 3|8, as hereinbefore set forth, and assuming that relays 420 and 450 are not operated at this time, relay 3|a operates over the previously described chain circuit to battery on the left back contact and armature of relay 450. Relay 3|9, in operating, operates relay 320 in an obvious circuit, and removes the ground from the chain circuit extending over the right contacts of relay 4|9, corresponding relays of other intermediate switches, and right front contact of relay 409, thereby preventing the operation of relays 420 and 450 should a call be extended to switches P2 or P3 at this time. Relay 320, in operating, operates relays 32| and 322 locally, and operates relay 60| of the link-trunk selector LTS2 in a circuit from ground over the inner front contact of relay 30|, lower contacts of the off-normal springs 306, right front contact of relay 320, left front Contact of relay 3|9, brush 355 and second terminal of its associated bank, to battery through the winding of relay 50 Relay 32|, in operating-connects ground over its front contacts to conductors 326, 321 and 328, thereby grounding the lowest make contact of every set of contacts in the vertical and horizontal rows of switch PI. Relay 322, in operating, connects battery to the windings of horizontal magnets 323, 324 and 325. Relay 60|, in operating, associates the trunks outgoing to the succeeding stage from the selected level of each secondary switch, in this case the second level since the digit 2 was dialed, with the link circuit selector LCS. Assuming that the trunk T|2 is busy and has ground connected to its sleeve conductor 103 from the succeeding stage, the iirst link circuit selector relay 50| operates in a circuit from battery through its winding, over the fourth inner make contact of relay 60|, conductor 602, to ground over sleeve conductor 103. Relay 50|, in operating, opens the circuit over its back contact and the neXt-to-inner front contact of relay 60|, to the winding of horizontal magnet 104 ofV switch Si, thereby preventing the operation of magnet 104 which would result in the subsequent connection to the busy trunk Tl 2.

The winding of relay 503 is connected over the outer front contact of the previously operated relay 60I, and over conductor 604, to the sleeve conductor 8|3 of trunk T|8 of switch S3. Assuming that trunk T|1 is idle, relay 503 does not operate since there is no ground on conductor 8|3. Upon the previous operation of relay 60|, a circuit was closed from ground Over the inner front contact of that relay to battery through the windings of the slow-to-operate relay 506 and the rotary magnet 551.Y The energizing of magnet 501 does not cause any operation since the mechanism of Vswitch A is such that brush 508 does not step until its rotary magnet 531Y is deenergized.

VRelay 50i-3, operating after an interval, closes a circuit from ground over its front contact, brush 508, iirst terminal of its associatedbank, conductor 5534, armature and front contact of relay 50|, armature and back contact of relay 503, conductor 505, third outer front contact of relay 60|, conductor E03, to battery through the winding of horizontal magnet 804 of switch S3. Relay 506 is slow-to-operate to provide an interval suflicient for the selection of a link to a secondary switch having an idle trunk before ground is connected to conductor 500, thereby preventing the operation of the horizontal magnet of any other secondary switch. Y

Horizontal magnet 804, operating over the circuit previously traced, prepares the sets of contacts in the middle row of switch S3 for operation, and operates relay 805 in an obvious circuit. Relay 305, in operating, connects ground to the upper windings of vertical magnets 003, 801 and 808. As previously set forth, the operation of relay 322 associated with switch P| connected battery to the windings of the horizontal magnets 323, 324 and 325 of that switch. With ground now connected to the windings of the vertical magnets of switch S3, a circuit is completed from ground through the upper winding of vertical magnet 806, over conductor 809, to battery through the winding of horizontal magnet 325 of switch Pl, and these magnets operate in series. It will be obvious that, although battery is connected to the windings of horizontal magnets 323 and 324 of switch Pl at this time, these magnets cannot operate since they connect over conductors V329 and 330, to switches Sl and S2 respectively, and no ground is connected to the upper windings of vertical magnets of switches Sl and S2 at this time. Similarly, although the upper windings of all vertical magnets of switch S3 are grounded simultaneously, magnets 801 and 808 cannot operate since they connect to switches P2 and P3 respectively, over conductors 3M and 8 i5, and no battery is connected to the horizontal magnets of switches P2 and P3 at this time.

The aforementioned operation of horizontal magnet 804 of switch S3, in addition to operating relay 805, also prepares the middle horizontal row of contact sets of that switch for operation. Therefore, upon the operation of vertical magnet 800, the middle set of contacts in the rst vertical row of switch S3 operate. The operation of horizontal magnet 325 of switch PI prepares the set of contacts in the lowest horizontal row in switch Pl for operation, and in addition, closes a circuit from ground over its front contact, left back contact of relay 305, left outer front contact of relay 3i3, lower inner front contact of relay 301, to battery over the inner back contact and through the winding of vertical magnet 302. Magnet 302,

vand 8| 6 of switch S3, to tip conductor 3|| `and ring conductor 8|2 respectively, of trunk TlS.

Vertical magnet302 of switch Pl, in operating, also opens theY circuit through the windings; or" relay 30 and causes that relay to release. Relay 30I, in releasing, removes the ground over its inner front contact from the windings of relays 3|8 and 60|, causing these relays to release.

In addition, relay 30| in releasing removes the ground from the winding of slow-to-release relay 301, and energizes the level selector release magnet 3| 1 in a circuit from battery through the winding of the magnet, upper make Contact of springs 303, inner left front contact of relay 3l3, lower outer front contact of relay 301, to ground over the back contact of relay 30 l. Release magnet 3|1, in energizing, restores brushes 3|5 and 3|6 to their normal position and causes the offnormal contacts 306 to restore to the unopelated position. Relay 301, being slow-to-release, provides for holding vertical magnet 302 operated and for maintaining the busy Vground on the sleeve conductor of trunk T untilthe selected trunk circuit of the succeeding stage has had time to function and return a ground for this purpose. This holding ground Vfrom the succeeding stage is traceable over sleeve conductor 3|3 of trunk T|8, cross-point 8|1, conductor 8|8, cross-point 335 of switch Pl, to sleeve conductor 308 to trunk Ti, and over the inner front contact and through the winding of magnet 302 to battery. After an interval, relay 301 releases and removesY the ground from conductor 336, this conductor having since been grounded from the succeeding stage as set forth above. Relay 301, in releasing, also opens the holding circuit for relay 3|3, opens the circuit through the winding of release magnet 3|1 of the level selector switch LSI, and removes the ground over its upper outer front contact and the neXt-to-inner back contacts of vertical magnets 309 and 3|0 from sleeve conductors 3|| and 3|2 of trunks T2 and T3 thereby removing the busy condition from these trunks.

Relay 3|0, in releasing, opens the operating circuits for relays 3|3 and 3|9, causing these relays to release. Relay 3|9, in releasing, o-pens the circuit through the winding of relay 320 and again connects ground to the sequence relay chain circuit extending over the normally closed right contacts of relays, 3|9, 4|9 and 449. Relay 320, in releasing, releases relays 32| and 322. Relay 32|, in releasing, removes the ground from conductors 32B, 321 and 323. The purpose for which these conductors were grounded will be set forth in detail subsequently. Relay 322 in releasing, removes the battery from the windings of horizontal magnets 323, 324 and 325. Magnet 325 releases and the lowest set of contacts in the first vertical row of switch PI are held in the operated position by vertical magnet 302 which is locked to ground from the succeeding stage.

Relay 60|,releasing upon the release of relay 30| as previously described, opens the circuit through the windings of relays 50| and 506, winding of rotary magnet 501, and winding of horizontal magnet 804 of secondary switch S3. Re-

lay 53| releases and closes, in part, the operat- 4The middle set of contacts in the rst vertical row in switch S3 are now held operated under control Vof vertical magnet 806 which is locked through its lower winding to ground supplied over sleeve conductor 8l3 from the succeeding stage. `Relay 505, in releasing, removes the ground from brush 508 of switch A. Rotary magnet 501, in deenergizing, causes brush 508 to step to the second contact of its associated terminal bank.

Allotter switch A which, together with the link circuit selector relays 50|, 502 and 503, is common to the link-trunk selectors LTSl, LTSZ and LTS3. Each time a connection is extended through this stage, the release of the particular link-trunk selector relay used deenergizes rotary magnet 501 and the brush of switch A advances to the next lower terminal of its associated terminal bank. As it successively advances, one step for each extended connection, brush 533 perpares the operating circuits for the horizontal magnets of the i'lrst to tenth or last secondary switch consecutively, thereby changing the order of the first choice trunk in any group. In this foregoing manner, an even distributionof traffic through the groups of trunks outgoing from the various corresponding levels of the secondary switches is obtained.

Since only magnets 302 and 856 remain operated, the common equipment associated with the primary and secondary switches is ready to receive another incoming call. At the conclusion Y of the call extended through this stage from incoming trunk Tl over the outgoing trunk Til, ground is removed from sleeve conductor 8|3 by the succeeding stage thereby opening the locking circuits for magnets 332 and 806. Magnet 302, in releasing, restores the lowest set of contacts of the rst vertical row in primary switch Pi'. Magnet 806, in releasing, restores the middle set of contacts of the irst vertical row in secondary switch S3 and this group-selecting stage is thereby restored to normal. For calls Vincoming over trunks T4 to T6 inclusive, or over trunks T1 to T9 inclusive, primary switches P2 or P3, respectively, function in the same manner as set forth for switch Pl. switches Sl vand S2 function in the manner identical with the operation of switch S3. On a call incoming to switch P2 the operation of sequence relay 4| 3 opens the chain circuit ground to prevent the operation of relay 449, on a simultaneous call incoming to switch P3, from operating relay 450. Similarly, the operationrof relay 423 of switch P2 opens the operating circuit for relay 319, to prevent the operation of relays 3i@ and 320 on a simultaneous call incoming to switch Pl. On a call incoming to switch P3, the operation of relay 450 opens the operating circuits for relays 3|3, M3 and corresponding relays of the other intermediate primary switches of the-group (not shown).

As previously set forth, on a call being extended through this stage from primary switch `PI, the operation of relay 3|9 opens the ground Similarly, secondary mally closed right contacts of relays 3|9, 4|9 and 449. Assume another call, incoming to this stage over a trunk appearing in primary switch P2, before the. call incoming to switch P| is extended to the succeeding stage. In response to dial pulses over the trunk incoming to switch P2, level selector LSZ will step its brushes to the terminals of its associated bank, the number of steps taken corresponding to the dialed digit. Upon the rst step of the brushes, the off-normal springs (not shown) of level selector LSZ operate and close the operating circuit for relay 4|9. Relay 4|9 operates but, since there is no ground on its right front contact, it does not cause relay 420 to operate. The call over switch P2 is not cut through to the link-trunk selector since ground over the right front contact of relay 420, and over brush 4|5, is required to complete the operating circuit for the link-trunk selector relay, such as relay 60|. When the call incoming over switch PE is extended to the succeeding stage, relay 3|9 releases and closes ground to the sequence chain circuit over its normally closed right contacts, thereby permitting relay 420 to operate. Relay 420, in operating, completes the operating circuit for the link-trunk selector relay associated with the particular level dialed, and the call incoming to switch P2 is extended in the manner identical with that hereinbefore described for the call incoming to switch PI.

On a call incoming over trunk T1, T8 or T9, the sequence relays 449 and 450 associated with switch P3 remain operated until the call has been extended to the succeeding stage. RelayV 450, in operating, removes the battery over its left back contact from the chain circuit extending to the winding of relay 4 I9, and over the left back contact of relay 420 to the winding of relay 3|9. Calls incoming at this time over trunks appearing in primary switches PI and P2 are not connected through to a link-trunk selector circuit since relays 3|9 and 4|9 cannot operate. After the call incoming over switch P3 is extended to the succeeding stage, relays 449 and 450 release. Relay 450, in releasing, reconnects battery to the windings of relays 3|9 and 4|9. Relay 3|9 operates, in turn operating relay 320 thereby closing the operating circuit for the associated linktrunk selector relay over brush 3|5 of level selector LSI. The call incoming over switch PI is now extended through the stage in the manner hereinbefore described. Relay 3|9, in operating, also removes ground from the chain circuit extending over the right contacts of relays 4|9 and 449. Therefore, following the release of relay 450, the operation of relay 4|9 does not operate relay 420. The call incoming over switch P2 now awaits the release of relay 3|9 before being connested to a link-trunk selector for extension through this stage.

When the lowest set of springs in the first vertical row in switch P| op-erated during the extension of the call incoming over trunk Tl as hereinbefore .set forth, a circuit was closed from the outer front contact of relay 32|, over crosspoint 331, conductor 338, to the next-to-outer armatures of link-trunk selector relays 509, 60| and 606, and to the winding of relay 8l9'. However, since relay 32| released as soon as the connection incoming over trunk TI was extended to the succeeding stage relay 8l9 di-d not operate. Assume now that with connection from trunk TI to trunk T|8 still established, another call, over trunk T3, is incoming to switch PI. Relay 339 operates over the circuit throughfthe preceding stages and over the subscribers loop in the same manner as previously described for relay 30|. Relay 339, in operating, operates relay 340. Re-

lay 340, in operating, connects ground over its upper inner front contact to the sleeve conductor 3|2 of trunk T3 and also connects ground'over its upper outer front contact to sleeve conductor 3| of trunk T2, thereby making these trunks'busy to the preceding stage. Trunk TI, which at this time is already in use, has its sleeve conductor 308 grounded from the succeeding stage over Aa previously traced circuit.

Assume that on this call incoming over trunk T3, the digit 0 is dialed into this stage. Relay 339 therefore releases and reoperates ten times in response to the ten dial pulses corresponding to the digit 0. Under control of ground-pulses over the back contact of relay 339, over. the lower outer front contact of relay 340 and left back'con-' tact of relay 3I3, rotary magnet 394 advances brushes 3|5 and 3|6 of the level selector LSI to the tenth contacts of their associated terminal banks. springs 300, relay 3|8 operates in a circuit from battery through its winding, over the lower contacts of springs 306, to ground over the inner front Contact of relay 339. Relay 3|8, in operating, operates relay 3|3 locally, and, providing that no other call is being extended through any other primary switch of the group, operates relay 3|9 over a previously traced chain circuit. Relay 3| 9, in operating, operates relay 320 locally. Relay 320, in operating, operates relays 32| and 322 locally, and operates relay B96 of link-trunk selector circuit LTS3 in a circuit from ground over the inner front contact of relay 339, lower contacts of springs 306, right front contact of relay 320, left front contact of relay 349, brush 3 |5 and tenth terminal of its associated terminal bank, conductor 34|, to battery through the winding of relay 60S. Relay 32|, in operating, connects ground over conductors 326, 32'? and 328 to the lowest make contact of each set of contacts in switch Pl. Relay 322, in operating, connects battery to the windings of horizontal magnets 323, 324 and 325. Relays 696, in operating, associates the trunks outgoing to the succeeding stage from the lowest level (which corresponds to the dialed digit 0) of each secondary switch with the link circuit selector LCS.

Assume that, at this time, trunks T|3 and T|6 of switches Sl and S2, respectively, are both busy. Upon the operation of relay i506 therefore, relays 50| and 502 operate since the trunks associated with these relays are busy. The circuit for relay 50| may be traced from battery through the winding of the relay, fourth inner front contact and armature of relay 605, over conductor l, to ground from the succeeding stage over sleeve conductor '|05 of trunk T|3. Relay 532 operates in the circuit from Ybattery through its winding, over the seventh inner front contact and armature of relay 60B, conductorV 308, to ground from the succeeding stage over sleeve conductor 320 of trunk T|6.

Trunk T|9 of the last secondary switch of the group is assumed idle at this time but, since the link consisting of conductors 333, 334 and 8|8, which interconnects primary switch PI with secondary switch VS3 is being used on the call extending from incoming trunk TE to outgoing trunk T|8 as hereinbefore set forth, trunk T59 is therefore unavailable eventho-ugh idle. Relay 503 operates in a circuit from battery through its Upon the operation of the off-normalVY winding, over conductor 510, neXt-to-outer front contact and armature of relay 333, conductor 333,

cross-point 331, conductor 326, to ground over the outer front contact of relay 325. Relay 8I9 also operates in a circuit from battery'through its winding to the ground on conductor 338, the circuit for which has just been traced. Relays 53E, 532 and 533, in operating, open the circuits to horizontal magnets 133, 82l and 324 of secondary switches SI, S2 and S3 respectively, to prevent the operation of these magnets upon the operation of the slow-to-operate relay 536 the circuit for which was. closed by the operation of relay 606.

With trunks T43 and TIB busy, and trunk Tl!) unavailable since its associated link to switch Pl is in use, a chain circuit is closed from ground o-n conductor 101, over the two lowest cross-points or" whichever set of contacts in the lowest horizontal row in switch Sl is o-perated, over conductor 133, the two lowest cross-points of whichever set of contacts in the lowest horizontal row in switch S2 is operated, over conductor 822, outer make contact and armature of relay 8I9, conductor 323, tenth contact terminal and brush 3l3 of level selector LSI, through the right winding of relay 305, to battery over the right inner front contact ofrelay 3I8. Relay 335 operates in this aforementioned circuit and locks through its left winding from battery over the right outer front contact of relay 3l3, its left winding and left front contact, toground over the lower middle front contact of relay 348. Relay 335, in operating, removes the direct ground over its left outer back Contact from the lower winding of relay 339 and connects ground through the left winding of transformer 332, over its left outer armature and front contact to that point instead. The right winding of transformer 342 connects to a source of a characteristic busy tone over conductors 343 and 344. This busy tone is induced in the left winding of transformer 332 and thence to the calling subscriber since relay 339 is operated over the calling subscribers loop. Relay 305, in operating also opens the operating circuit for relay 3l9. Relay 3l9, in releasing, r'eleases relay 323, connects ground over its normally closed right contacts to the sequence chain circuit extending through the other primary switches of the group, and, in addition, opens the operating circuit for relay 636 which releases. Relay 329, in releasing, releases relays 32| and 322. Relay 32H, in releasing, removes ground from conductors 325, 321 and 323 thereby releasing relay 8l9 which was being held operated by the ground on conductor 326 over cross-point 331 and conductor 338. Relay 322, in releasing, opens the circuits from battery to horizontal magnets 323, 324 and 325. Relay 605, in releasing, opens the circuits through the windings of relays 531|, 592, 593 and 533, all of which release, thereby restoring the link-trunk selector LTS3 and the link selector LCS to normal. The release of relay 8I9 opens the chain circuit between conductors 822 and 823. Relays 395, 3l3, 3I8, 339 and 349 remain operated pending disconnection.

When the calling subscriber replaces the receiver on the switchhook upon receipt of the tone signal indicating that all paths are busy, relay 339 releases due to the opening of the subscribers loop by the switchhook contacts. With relay 339 released, release magnet 3 l1 of the level selector LSI is energized from battery through its winding, over the upper contacts of springs 333, left inner front contact of relay 3I3, lower outer front contact of slow-to-release relay 340, to ground over the back contact of relay 339. The energizing of magnet 3| 1 causes brushes 3l5 and 3|6 to return to normal at which time springs 336 restore to their unoperated position, thereby opening the circuits through the windings of relay and release magnet SI1. Relay 339, in releasing, also opens the circuit through the winding of relay 343'. Relay 343, in releasing, opens the locking circuits through the Winding of relay 313 and the left winding of relay 335 causing relays 335 and 3l3 torelease. The release of relay 340 also removes the ground over its upper front contacts from the sleeve conductors 3H and 3l2 of trunks T2 and T3 respectively, and these trunks may now be selected in the preceding stage by another call.

Relays 133 and 825, associated with secondary switches Sl and S2 respectively, perform the same function as hereinbefore described for relay 899 of switch S3. On a call being extended over any primary switch, relay 199 operates if the link between that primary switch and secondary switch Sl is in use. Similarly relay 825 operates if the link between that primary switch and secondary switch S2 is in use. The contacts of relays 139 and 825 parallel the twO lower multiple cross-points in each horizontal row oi contact sets in secondary switches SI and S2 respectively. The operation of either relay 103 or 825 causes the all-trunks-busy chain circuit to be extended over secondary switch SI or S2 since the outgoingtrunk in the desired level, although not busy, is unavailable due to its associated link being in use. Whenever all trunks outgoing from any level of the secondary switches are busy, or unavailable due to busy links, the all-trunks-busy chain circuit is completed over the entire secondary switch group'and provides for the operation 0f relay 335 yof switch PI or the corresponding relay of any other primary switch being used, and a busy tone is returned to the calling subscriber in the manner hereinbefore described.

What is claimed is:

l. In a telephone system, a plurality of groupselecting stages, means for sending successive series of impulses directly to the successive stages,`

primary and secondary switches at each said stages, each of said switches comprising rows of separately operable contacts and coacting bars for operating the same, and means responsive to the impulses incoming to a stage for selectively operating the bars of the primary and secondary switches thereat.

2. In a telephone system, a plurality of selecting stages each comprising a number of primary .and a number of secondary cross-bar switch-es, links interconnecting each primary and each secondary switch, means for sending successive series of designation impulses directly to the successive stages, and means responsive to the impulses incoming to a stage for selectively op-i' erating the primary and secondary switches thereat.

3. In a telephone system, a plurality of selecting stages each comprising a number of primary and a number of secondary cross-bar switches, links interconnecting each primary and each secondary switch, a plurality of groups of trunks outgoing from the secondary switches, each group having trunks appearing in a plurality of said secondary switches, means for sending successive series of designation impulses directly to the successive stages, and means responsive to the impulses incoming to a stage for selectively op" erating the primary and secondary switches thereat.

4. In a telephone system, a series of groupseiecting stages each comprising a plurality of primary and a plurality of secondary cross-bar switches, impulse receiving mechanism associated with each of said stages, means for sending the successive series of impulses of a wanted designation directly to the impulse receiving mechanisms at the corresponding stages, and means responsive to the receiving mechanism at each stage for selectively operating the primary and secondary switches thereat.

5. In combination, serially related group-selecting stages each comprising a plurality of primary and a plurality of secondary cross-bar switches, a plurality of trunks incoming to each of said primary switches, impulse receiving mechanisms, each serving to receive the impulses incoming over any one of the trunks appearing in a primary switch, means for sending the successive series of impulses of a wanted number directly to the mechanisms at the corresponding stages, and means controlled by said mechanisms for operating the primary and secondary switches at the respective stages.,

6. In combination, serially related group-selecting stages each comprising a plurality of primary and a plurality of secondary cross-bar switches, a plurality of trunks incoming to each of said primary switches, impulse receiving mechanisms, each serving to receive the impulses incoming over any one of the trunks appearing in a primary switch, means for sending the successive series of impulses of a wanted number directly to the mechanisms at the corresponding stage-` means effective when impulses are being received over one oi said trunks for rendering busy all other trunks incoming to the same primary' switch, and means controlled by said mechanisms for operating the primary and secondary switches at the respective stages.

'7. In combination, a group selecting stage comprising a plurality of primary and a plurality of secondary cross-bar switches, groups of incoming trunks, each group appearing in a separate one of said primary switches, trunks outgoing from said secondary switches, links interconnecting the primary and .secondaryY switches, impulse receiving devices individual respectively to said primary switches and responsive to a call on one of the incoming trunks for selectively operating the corresponding primary switch and one of said secondary switches to extend the call to an outgoing trunk and means effective when a number of incoming calls appear simultaneously for causing said calls to be extended one at a time through said switches to the outgoing trunks.

8. In a telephone system, a group-selecting stage comprising a plurality of primary and a plurality or" secondary switches, trunks incoming to said primary switches, trunks outgoing from said secondary switches, link circuits interconnecting each primary switch with each of the several secondary switches, and means for testing the outgoing trunks and the link circuits comprising a test circuit extending to each of said outgoing trunks and a test circuit for each of the link circuits extending through contacts of the corresponding primary switches.

9. In a telephone system, a group-selecting stage having primary switches and secondary switches thereat, trunks incoming to the primary switches, trunks outgoing from the secondary switches, link circuits, each primary switch having one of said link circuits extending to each of the secondary switches, test relays for testing the condition of said outgoing trunks. and the condition of said link circuits, a test circuit for each outgoing trunk extending to the winding of a particular test relay corresponding thereto, a test cir-cuit for each of the links having access to such outgoing trunk extending to the winding of said relay, and means for closing the test circuit 01 any one of said links through contacts of the corresponding primary switch.

i0. In a telephone system, a group-selecting stageI comprising a plurality of primary cross-bar switches and a plurality of secondary cross-bar switches, link circuits interconnecting said primary and secondary switches, operating magnets for said primary switches, each magnet individual to a particular one of said link circuits, operating magnets for said secondary switches, each magnet individual to a particular one of said link circuits, and means for applying a source of potential to a plurality of magnets at said secondary switches and to a plurality of'magnets at said primary switches to cause the simultaneous operation in a series circuit of a desired magnet at the secondary switch vand a desired magnet at the primary switch.

ll. In a telephone system, a plurality of primary cross-bar selector switches, a plurality of secondary Vcross-bar selector switches, links interconnecting said switches, each primary switch having one oiA said link circuits extending to each of said secondary switches, operating magnets at said primary switches individual to the respecive link circuits, operatingmagnets for the secondary switches individual to the respective link circuits, a source of battery potential, Vmeans for applying one pole of said battery to the windings of the secondary magnets for all link circuits incoming to a particularsecondary switch, and means for applying the opposite pole of battery to the windings of the magnets of the primary switches individual to the respective link circuits extending to said particular secondary switch.

STANLEY FOUSHEE NELSON. FRANK FOSTER SHIPLEY. 

